Rocket propulsion method



July 7, 1959 A. ZLETZ ETAL ROCKET PROPULSION METHbD Filed Dec'. 15. 1953INVENTORS: Alex Z/efz Don R. Carnwdy ATTORNEY United States Patent2,893,202, v, ROCKET PROPULSION METHOD Alex Zletz, Park Forest, and DonER. Carrnody, Crete,

lll., assignors to Standard Oil Company, Chicago, 11]., a corporation ofIndiana This invention relatestogas generation and rocket propulsion.More particularly. the invention relates to a liquid rocket fuel whichissuitable for use at very low atmospheric temperatures.- a s aBipropellant rockets have assumed a larger and larger place in themilitary and commercial fields both in missiles and in the assistedtake-off of aircraft. In the bipropellant rocket a liquid fuel-and aliquid oxidizer are injected separately and substantially simultaneouslyinto the combustion chamber of the rocket motor; the fuel and oxidizerignite hypergolically. or are ignited by an external system such as aspark plug and burn to form a large volume of gases at high temperature;these gases are passed from the combustion chamber by. wayof an exitorifice. M

A hypergolic fueloxidizer system ispreferred because an auxiliaryigniting system is thereby eliminated. In general the hypergolicactivity of liquid fuels and nitric acid oxidizers decreases,markedlywith lowering of the temperature of the fuel and oxidizer. Anair-to-air missile usually is exposed to-the extreme cold of highaltitudes for a period long enoughto substantially attain atmospherictemperature. At the altitudes now commonly utilized by militaryaircraft, temperatures on the order of about 65 F; are customary and 100F. is not uncommon. a

Not only must the fuel have a melting point. below about 65 F., but alsothe fuelshould have a viscosity low enough to flow readily throughthefuel lines at very low atmospheric temperatures, i.e., about 65 F. orlower. 'Y c The presently known liquid rocket fuels which fulfill theserequirements are extremely expensive; for most of these the-price isquoted in dollars per pound. More economical fuels which meet thesesevere requirements are desired in order to expand the field ofusefulness of rocket-propelled vehicles.

An object of this invention is a rocket fuel which is suitable for use,at vvery low atmospheric temperatures, i.e., below about 65 F. Anotherobject is a liquid rocket fuel which is suitable for use at very lowatmospheric temperatures and which is less expensive than the presentlyknown fuels. Still another object is a method of gas generation by thehypergolic reaction of a nitric acid oxidizer and a liquid rocket fuelat very low atmospheric temperatures. Yet another object is a method ofrocket propulsion by the hypergolic reaction of the nitric acid oxidizerand a liquid rocket fuel at very low atmospheric temperatures.

It has been found that a composition consisting essen tially of betweenabout 25 and about SO-volume percent of an aliphatic phosphin'e and theremainder an olefin containing between about 7 and 20 carbon atoms issuitable for use as a hypergolic rocket fuel with c'ertain nitric acidoxidizers at verylow atmospheric temperatures.

A. Monoaliphatic phosphines which contain not more than 16 carbon atoms,and

B. Dialiphatic phosphines which contain not more than 16 carbon atoms.

The above-defined fuel composition has satisfactory hypergolic activitywith certain nitric acid oxidizers, hereinafter defined, when the fueland the oxidizer at the moment of contact in the gas generation chamberor .the rocket motor are at a temperature below about 65 F.

Certain monoaliphatic phosphines, dialiphatic phosphines, trialiphaticphosphines and mixtures thereof are useful for the purposes of thisinvention. The term aliphatic as used herein is intended to includehydrocarbon groups selected from the class consisting of paraffins andolefins. Highly branched aliphatic groups have desirably lower freezingpoints than the straight chain or slightly branched groups. It ispreferred to use branched aliphatic groups. The pressure of unsaturatedlinkages in the aliphatic group improves the hypergolic activity.

The hypergolic activity of the various aliphatic phosphines is dependentupon the number of aliphatic groups, upon the total number of carbonatoms contained in the aliphatic phosphine, and upon the number ofcarbon atoms contained in each of the aliphatic groups. In order toobtain a mixed fuel which is usable at temperatures as low as 65 F., itis necessary that the monoaliphatic phosphines contain not more than 16carbon atoms. The phosphines which contain two aliphatic substituents,i.e., dialiphatic phosphines, must contain not more than 16 carbon atomsin the molecule. Thus a dialiphatic phosphine which contains a 15 carbonatom side chain must not contain more than 1 carbon atom in the secondside chain. The completely substituted phosphines, i.e., trialiphaticphosphines are not particularly suitable for the purposes of thisinvention; however, small amounts of these may be tolerated along withmonoand di -aliphatic phosphines.

It is preferred to use the monoaliphatic phosphines or a natural mixtureof monoaliphatic phosphines and dialiphatic phosphines as obtained inthe reaction of PH and an olefin, i.e., not morethan about 20 molpercent of dialiphatic phosphine and a slight amount of trialiphaticphosphine.

The rocket fuel composition of this invention contains as the othercomponent a normally liquid olefin that is essentially non-hypergolicwith white fuming nitric acid at ordinary atmospheric temperatures, i.e,below about 80 F. (An essentially non-hypergolic hydrocargon is one thatdoes not react with nitric acid oxidizer to produce a visible flamealthough gaseous products may be prm duced.) In order to avoid boilingat the low pressure of high altitude, the olefin used herein contains atleast 7 carbon atoms. Satisfactory hypergolic activity of the blendrequires an olefin containing not more than 20 carbon atoms. Thepolymers formed by the homoor co-polymerization of propylene andbutylenes are the preferred olefins. Examples of these are propylenetrimer and tetramer; butylene dimer, trimer and tetramer;di-isobutylene; and propylene-butylene polymer containing 7 carbonatoms.

Several methods are known for the preparation of the aliphaticphosphines, e.g., the method of W. C. Davies and W. J. I ones asdescribed in LOhem. Soc. (London); p. 33 (1929); also, that of W. C.Davies in J. Chem. Soc. (London), p. 1043 (1933). Both of these methodsinvolvethe Grignard reaction. However, it is preferred 4 to use themethod described in US. Patent 2,584,112

least one member of the class consisting of:

which involves the reaction of phosphine, PH; and an olefin, in thepresence of an acid catalyst; or the same reactionin the presence of aperoxy catalyst.

7 The products from all of these methods of preparation contain minoramounts of impurities. These impurities have a favorable effect on thefreezing point of the aliphatic phosphines and appear to have nosubstantial adverse effect on hypergolic activity. It has also beenfound that the aliphatic p'hosphines which have been oxidized'to'aminorextent, e.g., 4 or 5%,are -usfful-as hypergolic fuels. It is intended toinclude within the scope "of'the invention the use of aliphaticphdsphines which contain minor amounts of impurities resulting from thepreparation thereof and also thosewhich contain ininor amounts 'ofoxidation products resulting from the oxidation of the aliphaticphosphine.

The preferred mixed fuel 'of this invention consists of a'ibl'end of 'a"monoaliphatic phosphine and the ol'efin' corresponding to the aliphaticgroup of the phosphine. To illustrate: A blend of dodecenes andmono(dodecyl) phosphine. v p

More particularly, the mixed fuel of this invention is prepared byreacting the desired olefin with'PH i'n' the presence of a non-oxidizingacid catalyst. The desired ratio of olefin to aliphatic pho'sphine inthe reaction product mixture is obtained by using a sufii'ci'en't excessof olefin. The other conditions are adjusted to produce an aliphaticphosphine product containing only a small amount of the; di-de'rivativ'eand only a slight amount of the tri derivative; the monoalipha'ticphosphine -form's' between 80 and 90 mol percent of the total aliphaticphos phine product.

The aliphatic phosphines are almost completely miseibl'e'in the normallyliquid olefins at temperatures below -'-l F. Also the blends possessgood viscosities at these very low temperatures. A fuel of satisfactoryhypergoh'c' activity at very low atmospheric temperature contains atleast about 25 volume percent of the defined aliphatic phosphine and theremainder the defined olefin. When'using about an equi-volume blend, themixed fuel has a' hypergolic activity at temperatures below about -65 F.substantially equal to that of the aliphatic phosphine' componentitself.

The rocket fi'iel composition of theinventio'n ishypergolic-at'ordi'nary temperatures, i.e., about 75 F., with mostnitric acid oxidizers. At temperatures on theorder ofO" F. it ishypergolic with nitric acid oxidizers containingas much as weightpercent of non-acidic materials. These non-acidic materials may be wateror pour point d'ep'ressors such' as potassium nitrite or sodium mtrate.At very low atmospheric temperatures such as --65 F., the nitric acidoxidizers are selected from the class consisting of red fuming nitricacid, nitric acidoleu'in mixtures and nitric acid alkanesulfonic acidmixture". The nitric acid-oleum mixtures consist of whitefurniiignit'ric acid and oleum, for example, an "80:20 mixture. Thenitric acid-alkanesulfonic acid mixtures m'a oensist of mixtures of WFNAand methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid,etc. Onlyenough o'leumor alkanesulfonic acid-is present togive afreezing point somewhat lower than the desired initial temperatureofoperation. Red fuming nitric'aeid containing at least about 16% of N 0is the preferred oxidizer at very low temperatures.

The results obtainable with the'mixed fuel of this invention areillustrated by the following"'example';

TESTl Commercial grade diisobutylene was carefully fractio'natdto obtainaheartcut' corresponding-tto'zpure 'diiso butylene. The purediisobut'ylene" was reacted worn, in: a: stainless steel bomb. Onehalf'm0'l o'f diisobutylene and 0.-5 mol of methane'sulfonic acidcatalyst we're"pl'aced in: the bomb at room temperature? one' half molof PH -g was added to the bomb; Theentire assembly-"was' ag'itated by arocker device, while the bomb was being heatedvto +8-5 C.;'th'e bombwasroc'ked for onefho'ur at +85 C. Thebomb' was permittedto'standovernight without" adding any further heat. The liquid contentswere removed from the bomb and washed with dilute aqueous NaCl to remove.methanesulfonic acid.

The neutralized liquid was distilled to remove diisobutylene. A fractioncorresponding to mono(diisobutyl)phosphine was taken overhead. Thisfraction boiled at 85.5 to 86.0 C. (88 mm. Hg) and had a melting pointof 70.0 to 69.5 C. The bottoms fraction comprised essentiallydi(diisobutyl)phosphine. The monofraction consistedof 0.28": mar. thebottoms fraction consisted of 0.06 mol. Thus the yield based onolefinwasj%. p v

The ignition delays of the mono di-isobutiyfiphosphine, blends of themonoderivative and diisobutylene, and a blend of mono-derivative andcommercial grade isooctane were determined at-various temperatures. (Theignition delay is d efined as the time between the mixing of the fueland the oxidizer and the appearance of a visible flame.) The ignitiondelays in this example were detennined by means; of 'an' a paratus whichpermitted thenreasurement of th :delay n milliseconds.The-ignition-delays were determrneti by cooling the-"fueband theoxidizer separately to the desired -te;r'n'per'a't'u e'. The oxidizer inthe"-+'7'5 F.: experiment was white tamingitric acid whic'hontaine'dabout 2 weight-person *o'f water. 'rhelcther experimeiits :werecarriedout= using id containing; 22 weight ercent of The data deriyed: in"these tests are set' oiit in The diisebiitytene: andis'ooct'ane'sliovtiedzno'hyprgolie activity with WFNA'at +75?- :In: an;air taair "ssile," an ignition delay of as" much as millis'e'coi'd's' istolerable: Preferably; ure-delay should be below 50 milliseconds. Theabove data-show that accept'able mixed fiuel can be obtained-b hlendin'gabout25voltlme-ypercentofaliphatie phusphine and the remainderanolefin-particularly 'the' blefin corresponding to th'ealiphatic-group.

The blend containi r'i equal volumes of aliphatic phosphine' -and olefinntially as good a fuelat the lower temperatures fas-the'purealiphaticphosfiine itself. Since this equal volume blend is essentially the e ualof the pure aliphati'e hosphine itself; there'- is no reason for usingnrore- -than this'amount of aliphatic hosphihe in the mixed fuel.Considerations of economy arid tl-ir us't require theuse 'ofithe leastamount of aliphatic ph'osphine consistent with the -ignition 'd elaydesired.

The completely unacceptable erformance of the isooctane "blend at 'lowertemp'eratures is most'su'rp'risi-ng in view of the compartively equalperformance ofitlie three blends at: -|T-7i5"lF. Andithis'showsanunpred-ictably favorabletinfiuence j'ofrat-single unsaturated bond iiithe diluent 'hydrocarbonion low temp'erature performan'cez v Ta'bll[Ignition delay, milliseconds] Temperature, .QMOll O- Mono-% Mono: 30%-Mon0=:'50%-; F. (iiils'obiityl) Diis'obutyljDiiscbuty'l Isaoetanerm'z,

:Phosphlne -ene: 60% :ene: 70% 1 15:7 29. 8 .2415 2 1.-2 59.1 v 300 2352No Ignition. 25.9 '83. 2'

Bywayofiilli stratioiithe composition o'tthisinvention is applied' to-"the 'pro'pulsi'on 0f" an'- a'ir to air -i'nissilb; The annexed figurewhich forms a p'artjo'f this spe'cificm tion: showsschematicallytheb'ipropellant' fuel system, themotor and other; partsofsuch. a imissile;

the figure vessel llgcontains' .a;--quanti tyof; gas at highapresstlre;t s s mu be. in r w r t t9 the oxidizerandthe fuel suitable ,gasesarenitrogen helium" H' em .h el" m 'is used as the inert gas. Helium fromel ll pas d1 through litieZ lZftihd lf 'gulateisjthe new of" to maintaina constant pressure beyond valve 13. From valve 13 helium is passedthrough lines 14 and 16 into vessel 17 and simultaneously through line18 into vessel 19.

Vessel 17 contains the oxidizer. Helium pressure forces the oxidizer outof vessel 17 through line 21 to valve 22. Valve 22 is a solenoidactuated throttling valve. Suitable electrical lines connect valve 22 toan electrical source and operating switch (not shown) at the controlpanel of the aircraft. The oxidizer is passed through line 23 andinjector 24 into combustion chamber 26. Combustion chamber 26 isprovided with an outlet nozzle 27.

Vessel 19 contains the fuel. Vessels 17 and 19 are constructed towithstand the high pressure imposed by the helium gas. The gas pressureforces fuel from vesel 19 through line 28 to solenoid actuatedthrottling valve 29. Valve 29 is similar in construction and inactuation to valve 22. The fuel is passed through line 31 and injector32 into combustion chamber 26.

Valves 22 and 29 are of such a size and setting that a predeterminedratio of oxidizer-to-fuel is passed into combustion chamber 26.Injectors 24 and 32 are so arranged that the streams of oxidizer andfuel converge and contact each other forcibly, resulting in a verythorough intermingling of the fuel and the oxidizer.

The missile is launched by activating the solenoids on valves 22 and 29.In this illustration 4.5 lbs. of 22% RFNA are introduced into combustionchamber 26 per pound of fuel. Herein the fuel consists of 45 volumepercent of a monoalkyl phosphine containing carbon atoms and 55 volumepercent of the corresponding decenes. The oxidizer and the fuel reactalmost instantaneously upon contact in the combustion chamber; a largevolume of very hot gas is produced in the combustion chamber, which gasescapes through orifice 27. The reaction from this expulsion of gasdrives the missile toward its target.

Thus having described the invention, what is claimed is.

l. A method of rocket propulsion, which method comprises injectingseparately and substantially simultaneously into the combustion chamberof a rocket motor a nitric acid oxidizer selected from the groupconsisting of white fuming nitric acid and red fuming nitric acid and ahypergolic liquid fuel consisting essentially of about equal volumes ofmono(di-isobutyl)phosphine and diisobutylene, in an amount and at a ratesufiicient to initiate a hypengolic reaction with and to supportcombustion of the fuel.

2. The method of claim 1 wherein said oxidizer is red fuming nitricacid.

References Cited in the file of this patent UNITED STATES PATENTS 53,695Somes Apr. 3, 1866 2,368,866 Nygaard et al Feb. 6, 1945 2,573,471 Malinaet al. Oct. 30, 1951 2,584,112 Brown Feb. 5, 1952 OTHER REFERENCESJournal of the American Rocket Society, No. 72, December 1947, PP. 12,17, 21, 31-33.

1. A METHOD OF ROCKET PROPULSION, WHICH METHOD COMPRISES INJECTINGSEPARATELY AND SUBSTANTIALLY SIMULSTANEOUSLY INTO THE COMBUSTION CHAMBEROF A ROCKET MOTOR A NITRIC ACID OXIDIZER SELECTED FROM THE GROUPCONSISTING OF WHITE FUMING NITRIC ACID AND RED FUNING NITRIC ACID AND AHYPERGOLIC LIQUID FUEL CONSISTING ESSENTIALLY OF ABOUT EQUAL VOLUMES OFMONO (DI-ISOBUTYL) PHOSPHINE AND DIISOBUTYLENE, IN AN AMOUNT AND AT ARATE SUFFICIENT OT INITIATE A HYPERGOLIC REACTION WITH AND TO SUPPORTCOMBUSTION OF THE FUEL.